1. Field of the Invention
The present invention relates to methods of manufacturing silicon carbide (for example, thin films and ingots) employed as a substrate material in semiconductor devices and X-ray masks, chiefly silicon carbide employed in the components of semiconductor manufacturing devices, dummy wafers employed in semiconductor element manufacturing steps, and silicon carbide structural members (for example, heaters, anticorrosion products (screws, bearings), and the like).
2. Related Art
Silicon carbide is a semiconductor with a broad forbidden bandwidth of 2.2 eV or greater and is a thermally, chemically, and mechanically stable crystal. Further, due to high thermal conductivity, its application as a semiconductor material under conditions of high frequency, high power, high temperature, and the like is anticipated.
Methods of manufacturing silicon carbide include reacting coke and silicon on a heated carbon surface and precipitating silicon carbide on a carbon surface (the Atchison method); heating and sublimating silicon carbide formed by the Atchison method and recrystallizing it (sublimation method, improved Reilly method); the liquid deposition method in which silicon is melted in a carbon crucible and the suspended carbon and silicon are reacted in the crucible while drawing the product upward; and the like.
Methods of manufacturing silicon carbide include reacting coke and silicon on a heated carbon surface and precipitating silicon carbide on a carbon surface (the Acheson method): heating and sublimating silicon carbide formed by the Acheson method and recrystallizing it (sublimation method, improved Lely method): the liquid deposition method in which silicon is melted in a carbon crucible and the suspended carbon and silicon are reacted in the crucible while drawing the product upward: and the like.
Although the Acheson method produces inexpensive, large quantities of silicon carbide, the precipitating silicon carbide is amorphous, comprising crystalline polymorphism and large quantities of impurities. In particular, this method cannot be employed to manufacture semiconductor materials in which defects and impurities are problematic.
The improved Lely method reduces the problems of crystalline polymorphism. amorphism, and the like associated with the Acheson method. However, it is difficult to reduce the impurities incorporated into the crystal, and increasing the area of the crystal and decreasing the number of defects are no simple tasks.
The method that is generally employed to reduce the crystal defects and impurities that are problematic in the improved Lely method is to use CVD or ALE to epitaxially grow silicon carbide while reducing the defect density and impurities on a silicon carbide substrate obtained by the improved Lely method. However, since the area of the crystals obtained by these methods is limited to the area of the silicon carbide obtained by the improved Lely method, large-area. high quality silicon carbide cannot be obtained.
To increase the area of silicon carbide, the general method has been devised of using CVD of ALE to heteroepitaxially grow a silicon carbide layer on a single crystal silicon substrate employed as a semiconductor material. However, high concentrations of defects are produced at the interface of the silicon substrate and the silicon carbide. Thus, the quality of the crystal is poorer than that of epitaxially grown silicon carbide layers formed on silicon carbide substrates obtained by the improved Lely method. When employing heteroepitaxial growth, crystal quality can be improved by increasing the thickness of the film of silicon carbide being grown. However, since the rate of silicon carbide growth by CVD of ALE is extremely low, the application of silicon carbide obtained by heteroepitaxial growth is currently impeded.
The rate of growth of silicon carbide can be increased to some extent by increasing the partial pressure of the starting gasses using CVD. However, the faster the growth rate, the more crystal defects tend to increase in the silicon carbide. Since the ALE method requires that a certain quantity of atoms or molecules be uniformly adsorbed to the substrate surface under thermal equilibrium, increasing the growth rate of silicon carbide by increasing the amount of gas being fed as is done in CVD is undesirable.
Accordingly, the object of the present invention is to provide a method of manufacturing silicon carbide affording adequate ease of production by increasing the growth rate of silicon carbide in gas vapor growth without increasing crystal defects.
That is, for example, a further object of the present invention is to provide a method of manufacturing silicon carbide of a quality suitable for use as a semiconductor element material with fewer crystal defects and affording adequate ease of production even in heteroepitaxial growth employing a substrate other than silicon carbide. A further object of the manufacturing method of the present invention is to obtain silicon carbide not just as a thin film, but also as an ingot or structural member.
A still further object of the present invention is to provide silicon carbide (not just thin films, but also ingots and structural members) having heretofore unseen dimensions (bores) in the form of silicon carbide of a quality suitable for use as a semiconductor element material with reduced crystal defects.
Yet another object of the present invention is to provide a semiconductor element employing the above-described silicon carbide as a substrate, and to provide a method of manufacturing composite materials employing the above-described silicon carbide as seed crystal.
The aforementioned objects can be achieved by the present invention as follows.
In accordance with the present invention, there is provided a method of manufacturing silicon carbide by forming silicon carbide from an atmosphere containing a silicon carbide feedstock gas on a substrate surface, characterized in that:
said silicon carbide feedstock gas comprises at least a silicon source gas and a carbon source gas;
the partial pressure ps of said silicon source gas in said atmosphere is constant (with ps greater than 0), the partial pressure of said carbon source gas in said atmosphere consists of a state of pc1 and a state pc2
(where pc1 and pc2 denote partial pressures of said carbon source gas, pc1 greater than pc2, and the partial pressure ratio (pc1/ps) falls within a range of 1-10 times the sticking coefficient ratio (Sc/Sc), the partial pressure ratio (pc2/ps) falls within a range of less than one time the sticking coefficient ratio (Sc/Sc)
(where Sc denotes the sticking coefficient of silicon source gas to the silicon carbide substrate at the substrate temperature during formation of said silicon carbide, and Sc denotes the sticking coefficient of carbon source gas to the silicon carbide substrate at the substrate temperature during the forming of said silicon carbide))
that are repeated in alternating fashion (referred to as condition 1 below); or
the partial pressure ps of said silicon source gas in said atmosphere is constant (with ps greater than 0), the partial pressure of said carbon source gas in said atmosphere consists of a state of pc1 and a state pc2
(where pc1 and pc2 denote partial pressures of said carbon source gas, pc1 greater than pc2, and the partial pressure ratio (pc1/ps) falls within a range of 1-10 times the sticking coefficient ratio (Sc/Sc), the partial pressure ratio (pc2/ps) falls within a range of less than one time the sticking coefficient ratio (Sc/Sc)
(where Sc denotes the sticking coefficient of silicon source gas to the silicon carbide substrate at the substrate temperature during formation of said silicon carbide, and Sc denotes the sticking coefficient of carbon source gas to the silicon carbide substrate at the substrate temperature during the forming of said silicon carbide))
the partial pressure ps of said silicon source gas in said atmosphere is constant (with ps greater than 0). the partial pressure of said carbon source gas in said atmosphere consists of a state of pc1 and a state pc2
(where ps1 and ps2 denote partial pressures of said silicon source gas, ps1 greater than ps2, and the partial pressure ratio (pc/ps1) falls within a range of 1-10 times the sticking coefficient ratio (Sc/Sc), the partial pressure ratio (pc/ps2) falls within a range of less than one time the sticking coefficient ratio (Sc/Sc)
(where Sc denotes the sticking coefficient of silicon source gas to the silicon carbide substrate at the substrate temperature during formation of said silicon carbide, and Sc denotes the sticking coefficient of carbon source gas to the silicon carbide substrate at the substrate temperature during the forming of said silicon carbide))
that are repeated in alternating fashion (referred to as condition 2 below).
In the above manufacturing method of silicon carbide, the followings are preferred.
In condition 1, pc1 and pc2 each continue for a prescribed period, and in condition 2, ps1 and ps2 each continue for a prescribed period.
Silicon carbide is formed on a substrate the temperature of which is not less than 900xc2x0 C.
The above silicon source gas is at least one member selected from the group consisting of SiH4, Si2H6, SiCl4, SiHCl3, SiH2Cl2, Si(CH3)4, SiH2(CH3)2, SiH(CH3)3, and Si2(CH3)6, and said carbon source gas is at least one member selected from the group consisting of CH4, C3H8, C2H5, C2H6, C2H2, C2H4, CCl4, CHF3, and CF4.
Pc2 or ps1 is essentially 0.
Pc2 is essentially 0, the time during which the partial pressure of the carbon source gas is set to pc1 is 0.1-30 seconds, and the time during which the partial pressure of the carbon source gas is set to pc2 is 0.1-30 seconds.
The present invention further relates to a method of manufacturing silicon carbide characterized in that the silicon carbide manufactured in any of claims 1-6 is employed as seed crystal and in that silicon carbide is formed on said seed crystal by vapor phase epitaxy. sublimation recrystallization, or liquid phase epitaxy.
In the above manufacturing method of silicon carbide, the preferred is that silicon carbide blocks 4-6 inches are formed by vapor phase epitaxy, sublimation recrystallization, or liquid phase epitaxy.
The present invention further relates to a silicon carbide block characterized by having a bore of 4-6 inches.
In the above silicon carbide block, the preferred is that the planar defect density is not more than 103/cm2.
The present invention further relates to a semiconductor element employing as substrate the silicon carbide block described above.
The present invention further relates to a method of manufacturing composite materials characterized in that silicon carbide manufactured by the above-mentioned method is employed as seed crystal and diamond and/or gallium nitride is formed on said seed crystal.